1. Field of the Disclosure
The disclosure generally relates to a voltage supply circuit, and more particularly, to a voltage supply circuit capable of selectively supplying different supply voltages.
2. Description of Related Art
Along with the development of communication and network technologies, telephone devices have been made capable of transmitting audio data (and accordingly making phone calls) through the Internet. When a user makes a phone call by using an IP (Voice over Internet Protocol) phone, the IP phone digitizes and compresses the audio data and then transmits the processed data to a target device through the Internet. The target device decompresses and restores the received audio data and passes it to the other party of the conversation. Many IP phones have been developed since they require no conventional cable network for transmitting data, offer high security level, and are suitable for long-distance communications.
When an IP phone is designed, a voltage amplifier is usually adopted for driving the speaker, and the voltage amplifier requires an external voltage source to work properly. When a user adjusts the volume of the IP phone, the power consumed by the voltage amplifier changes accordingly. However, if the external voltage source remains unchanged, unnecessary power consumption may be caused in the IP phone when the volume is changed. Thereby, how to adjust the voltage supply of a voltage amplifier according to the volume level of an IP phone is one of the subjects to be resolved in the field.